Dynamic characteristics of pressure drop oscillation related to the compressible volume in a liquid cooling loop

Pressure drop oscillation is a universal dynamic instability mode occurring within the liquid cooling loop, which can result in a severe deterioration of the operation stability and heat transfer performance. There are two confusions regarding the triggering mechanism and flow hydrodynamics responsible for this phenomenon, which relate to the stiffness and the number of the compressible volumes. To address these issues, this study performed a series of experiments with the gas temperature, the position and the number of compressible volumes varied. The experimental results indicate that two forms of flow instability with and without the backflow phenomenon are triggered when the gas temperature in the upstream buffer tank exceeds that in the accumulator. An oscillatory phenomenon in the heat transfer coefficient is observed in the former instability mode. In addition, the presence of an upstream compressible volume is essential for the onset of pressure drop oscillation. Moreover, the stability of the cooling loop can be enhanced by relocating the compressible volume downstream of the microchannel heat sink. Subsequently, the dynamic flow characteristics and instability map of the cooling loop were investigated, which incorporates both the upstream and downstream compressible volumes. An overheating phenomenon is observed at the heating power of 40 W, and the instability form with the backflow behavior is eliminated. Compared to the single compressive volume case, the exit temperature and pressure drop exhibit substantial reductions with the maximum amplitudes decreasing by 76% and 75% respectively, the instability region shrinks consequently. Therefore, this work identifies two key measures for enhancing electronic device stability in the slug flow regime, which are regulating the gas temperature within the upstream volume and incorporating a downstream volume to dampen rapid pulsations induced by pressure drop oscillation or device power transients.